From WoWWiki

A demigod in the Warcraft universe is a being of great power, often the offspring of gods or other powerful beings. The most active demigod in mortal affairs has been Cenarius, the forest lord who taught druidic practices to the tauren and night elves.

Azerothian demigods have a strong connection to nature. Many of them, including Cenarius' father Malorne, perished in the War of the Ancients.

Also known as "Ancients", but not to be confused with the sentient tree beings also called Ancients.